Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

341
FXUS63 KLOT 121108
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
508 AM CST Mon Jan 12 2026

.KEY MESSAGES...

- Mild conditions are in store today through Tuesday before the
  pattern turns decidedly more wintry on Wednesday and beyond,
  with below normal temperatures and occasional periods of
  snow/snow showers.

- The main concern from a winter weather impacts perspective is
  Wednesday into Thursday, with wind-whipped snow showers during
  the day Wednesday likely followed by accumulating lake effect
  snow Wednesday night into Thursday morning, primarily for
  parts of northwest Indiana.

&&

.DISCUSSION...
Issued at 326 AM CST Mon Jan 12 2026

Through Tuesday:

The week will start off on a breezy and milder note, with
temperatures in the 40s both today and Tuesday. Some of the
warmest spots could even tag 50 briefly Tuesday afternoon. Dry
weather is expected into tonight, with the potential for
isolated sprinkles on Tuesday.

The upper level pattern features a broad trough across the
eastern CONUS early this morning, and ridging along the west
coast. A few low-amplitude short waves are evident in the
northwest flow from the Pacific Northwest into the Great
Lakes/Midwest region, the most notable across the northern
Lakes. This wave is currently producing some light snow well to
the northeast of the forecast area, and will not be a factor
locally. A couple of more subtle waves/speed maxima are noted
upstream of the area in GOES vapor imagery, and these will zip
southeast from the Northern Plains and across the area through
this afternoon. 00Z RAOBs from upstream sites depict fairly dry
low-levels across the region however, and the most visible
impact of these ripples will be to bring some passing high
clouds across the area. Otherwise, we`ll enjoy breezy low-level
southwest flow across the region (some gusts to around 25 mph
especially this morning) which will result in milder
temperatures in the low-mid 40s for the forecast area today.
Similar to Sunday night, we`ll likely lows in the low-mid 30s
this evening, with temps then holding fairly steady overnight.

Farther upstream, another short wave topping the western ridge
this morning is forecast to gradually amplify as it tracks
southeast toward the upper Midwest and northern Lakes region
tonight. Guidance indicates an associated sub-995 mb surface low
developing near Lake Superior by midday Tuesday, maintaining
and further inducing breezy southwest flow into the Midwest in
the process. While more significant precipitation is expected to
remain north/northeast of the forecast area late tonight into
Tuesday, some high-res guidance does generate some spotty light
QPF across the cwa mainly during Tuesday afternoon when deeper
large scale forcing strengthens. Despite the increasing ascent
however, low-level moisture return appears meager due to surface
ridging along the Gulf coast. Forecast soundings depict mainly
mid-level saturation with substantial dry air below, which
suggests mainly spotty light rain or sprinkles reaching the
surface here.

While cloud cover is expected to thicken on Thursday,
persistent southwest low-level warm advection flow should warm
temperatures a bit higher than today. Highs are expected in the
upper 40s in many areas, perhaps tagging 50 degrees in a few
spots.

Ratzer


Tuesday Night through Sunday:

A prolonged colder and unsettled northwest flow pattern will
set up in response to high amplitude ridging near the West
Coast. As the ridging further amplifies up to or north of the
Gulf of Alaska over the weekend into next week, this will
dislodge the coldest air mass we`ve seen since back in mid
December southward into the Midwest. The western ridging-
eastern troughing pattern exemplifies the positive phase of the
Pacific North American (PNA) teleconnection pattern, while the
high latitude blocking setting up near the Gulf of Alaska this
weekend and beyond represents the negative phase of the East
Pacific Oscillation (EPO) teleconnection pattern. The first
prominent short-wave/PV anomaly diving southward on Wednesday
will potentially bring an impactful lake effect snow event
downwind of southern or southeast Lake Michigan into Thursday.

Most of Tuesday night will be quiet and breezy with temperatures
still above normal. This will abruptly change by Wednesday
morning as the aforementioned robust PV anomaly dives southward
across the area in tandem with a secondary cold front passage
packing much stronger cold air advection. As winds shift to
north-northwesterly with gusts up to 30-40 mph, strong large
scale forcing will result in quickly blossoming snow showers
during the morning.

While there`s still some uncertainty in the westward extent of
sufficient moisture through the DGZ during the morning, run-to-
run continuity across the suite of global ensemble systems
remains good on the whole and supports the latest NBM
initialization`s 30-80% PoPs across our forecast area on
Wednesday morning (highest PoPs in northeast Illinois and
northwest Indiana and lowest PoPs towards northwest and central
Illinois). Depending on how this setup evolves from a
convergence and inversion height perspective, very steep low-
level lapse rates could yield embedded snow squalls. This would
be paired with temperatures falling quickly to the mid 20s to
lower 30s by the late morning. Initial melting on mild
antecedent pavement could conceivably be followed a flash freeze
scenario in a more strongly forced snow squall type regime. If
there ends up being scattered less intense wind-whipped snow
showers, that may serve to limit potential impacts.

The main notable change from the past few model cycles vs.
previous cycles is an eastward shift in the trajectory of the PV
anomaly. This would focus the highest snow shower coverage for
northern and central Illinois into the morning hours and then
could result in flurries at most for these areas by the
afternoon. Since this was a recent change, to account for a
plausible nudge back west some with the forcing, opted to hold
onto fairly expansive chance PoPs Wednesday afternoon. Higher
60-80% PoPs were confined to areas primarily near and east of
I-65 in northwest Indiana. Aside from the snow shower details,
it will be blustery and cold with wind chills falling into the
high single digits and lower teens prior to sunset.

As progged 850 mb temperatures plunge to -15 to -18C by early
Wednesday evening, increasingly favorable lake effect
thermodynamics will come into play. In fact, lake enhancement of
the snow showers may occur as early as the late AM and early
afternoon into northwest Indiana. However, the main event, so to
speak, looks to be towards and after sunset Wednesday. Based on
recent guidance trends, can`t ignore the eastward shift of the
focus of the PV anomaly and the lake induced convergence axis.
With this in mind, barring a shift back, the impactful
accumulating wind-blown lake effect snow threat will likely be
confined into portions of northwest Indiana. Some solutions
suggest the higher end threat could aim into LaPorte County,
though feel confident that at least some snow will fall into at
least northeastern Lake and most of Porter County.

Lake induced equilibrium levels as high as 8-12kft, 300-500 J/kg
of lake induced CAPE, convergence down the long axis of the
lake, and lingering synoptic lift are factors arguing for heavy
snowfall rates (and high ratios) within the heart of the band.
Given the recent shifts, opted to cap PoPs at 60-70% into
northeast Lake and Porter Counties (likely PoPs extending into
northern Jasper) through Thursday morning. Preliminarily will
advertise several inches of accumulation, though in reality, the
focus area will be much narrower (along with higher amounts in
the heart of the band/ie. double digits plausible). Of
significant concern as well is the very strong northerly winds
gusting to 40-45+ mph modeled in the heart of the band, so
blowing and drifting snow will likely exacerbate impacts. If the
lake effect snow threat continues to include portions of our
northwest Indiana counties as the event draws nearer, we may
very well need to hoist a watch within the next few cycles.

Any break following the probable lake effect snow event may be
short-lived, with signs pointing toward several additional
clipper type systems affecting the region through the weekend.
The first system Thursday night could have a period of
accumulating snow in the warm advection regime, followed by
waves of scattered snow showers Friday-Friday night. Maintained
broad-brushed chance PoPs peaking in the 30-60% range Thursday
night-Saturday given approximately that much ensemble member
support. Due to the deep northwest flow pattern, none of the
upcoming systems will have abundant moisture to work with.
Nonetheless, with temperatures trending to well below normal
to close out the week and through next weekend and beyond, any
minor accumulations can be expected to cause some travel
impacts. Sub-zero wind chills in the overnight-morning periods
are in the forecast Saturday night through Sunday night.

Castro

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 508 AM CST Mon Jan 12 2026

Aviation forecast concerns for the 12Z TAFs:

- Breezy southwest winds with gusts around 20 kt this morning,
  easing remainder of the day.

- Southwest gusts 20-25 kts develop predawn Tuesday. Could be a
  LLWS threat early Tuesday morning if surface gusts are slower
  to develop.

Northern IL and northwest IN terminals will see an extended
period of mainly southwest winds through this TAF cycle. Will
likely be some gustiness to around 20 kts this morning, though
this should ease gradually through this afternoon. Model
forecast soundings suggest fairly strong decoupling this
evening, which should limit wind gusts during the evening and
early overnight hours, after which development of a west-
southwesterly 40-45 kt low level jet is expected toward
daybreak Tuesday. Expectation is that surface winds will
increase gradually with at least some gustiness during this
time, mitigating the threat of LLWS. Based on this scenario did
not include LLWS in TAFs at this time, but will monitor surface
wind trends for early Tuesday for a possible LLWS inclusion if
needed (would be toward 12Z and after if needed). Surface wind
gusts to around 25 kts from the southwest appear likely later
Tuesday morning.

Otherwise, VFR conditions are expected through the period with
patchy high clouds today, thickening and lowering to a mid deck
later tonight/early Tuesday.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 9 AM CST this morning for Winthrop
     Harbor IL to Gary IN.

     Small Craft Advisory until noon CST today for Gary to Burns
     Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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